Iodine

Iodine is an essential trace element required for the synthesis of hormones, and the lack of it can also cause or contribute to the development of:

• Hypothyroidism
• Goiter
• Mental retardation
• Cretinism (severely stunted physical and mental growth and deafness due to untreated congenital hypothyroidism)
• Certain forms of cancer

Iodine is used by your thyroid gland to help regulate metabolism and development of both your skeleton and brain, among other things.

 Other tissues that absorb and use large amounts of iodine include:

Breasts	Salivary glands	Pancreas	Cerebral spinal fluid
Skin	Stomach	Brain	Thymus

Iodine deficiency, or insufficiency, in any of these tissues will lead to dysfunction of that tissue. Hence the following symptoms could provide clues that you're not getting enough iodine in your diet.
For example, iodine deficiency in:

• Salivary glands = inability to produce saliva, producing dry mouth
• Skin = dry skin, and lack of sweating. Three to four weeks of iodine supplementation will typically reverse this symptom, allowing your body to sweat normally again
• Brain = reduced alertness, and lowered IQ
• Muscles =  nodules, scar tissue, pain, fibrosis, fibromyalgia

Here are a few more interesting facts:

• In total, the human body can hold 1,500 mg of iodine
• Your thyroid can hold a maximum of 50 mg of iodine
• 20 percent of the iodine in your body is held in your skin (if your skin is depleted of iodine, you will not be able to sweat)
• 32 percent of your body's iodine stores are in your muscles (if muscles are depleted, pain and other fibromyalgia symptoms can develop)

Info taken from: http://articles.mercola.com/sites/articles/archive/2013/05/04/iodine-deficiency-affect-childs-brain-function.aspx